METHODS OF PREPARATION OF APPROXIMATE ESTIMATE:
Preliminary or approximate estimate is required for studies of various as- pects of work of project and for its administrative approval. It can decide, in case of commercial projects, whether the net income earned justifies the amount invested or not. The approximate estimate is prepared from the practical knowl- edge and cost of similar works. The estimate is accompanied by a report duely explaining necessity and utility of the project and with a site or layout plan. A percentage 5 to 10% is allowed for contingencies. The following are the meth- ods used for preparation of approximate estimates.
- a) Plinth area method
- b) Cubical contents methods c) Unit base
- a) Plinth area method: The cost of construction is determined by multiplying plinth area with plinth area rate. The area is obtained by multiplying length and breadth (outer dimensions of building). In fixing the plinth area rate, carefull observation and necessary enquiries are made in respect of quality and quantity aspect of materials and labour, type of foundation, hight of building, roof, wood work, fixtures, number of storeys ,
As per IS 3861-1966, the following areas include while calculating the plinth area of building.
- a) Area of walls at floor
- b) Internal shafts of sanitary installations not exceeding 0m2, lifts, air conditioning ducts etc.,
- c) Area of barsati at terrace level:
Barsati means any covered space open on one side constructed on one side constructed on terraced roof which is used as shelter during rainy season.
- d) Porches of non cantilever Areas which are not to include
- a) Area of
- b) Unenclosed
- c) Architectural bands, cornices ,
- d) Domes, towers projecting above terrace
- e) Box louvers and vertical
- b) Cubical Contents Method: This method is generally used for multistoreyed buildings. It is more accurate that the other two methods , plinth area method and unit base method. The cost of a structure is calculated approximately as the total cubical contents (Volume of buildings) multiplied by Local Cubic Rate. The volume of building is obtained by Length x breadth x depth or height. The length and breadth are measured out to out of walls excluding the plinth off set.
The cost of string course, cornice, carbelling etc., is neglected. The cost of building= volume of buildings x rate/ unit volume.
- c) Unit Base Method: According to this method the cost of structure is deter- mined by multiplying the total number of units with unit rate of each item. In case schools and colleges, the unit considered to be as ‘one student’ and in case of hospital, the unit is ‘one bed’. the unit rate is calculated by dividing the actual expenditure incured or cost of similar building in the nearby locality,